TY - GEN
T1 - Implementation of a piecewise-linear dynamic attenuator
AU - Shunhavanich, Picha
AU - Bennett, N. Robert
AU - Hsieh, Scott S.
AU - Pelc, Norbert J.
N1 - Funding Information:
This work was supported by the National Institutes of Health (U01EB017140) and the Anandamahidol Foundation. The experimental apparatus was supported by NIH Shared Instrument Grant S10-RR026714-01.
Publisher Copyright:
© 2018 SPIE.
PY - 2018
Y1 - 2018
N2 - A dynamic bowtie filter can modulate flux along both fan and view angles for reduced dose, scatter, and required detector dynamic range. Reducing the dynamic range requirement is crucial for photon counting detectors. One approach, the piecewise-linear attenuator (Hsieh and Pelc, Med Phys 2013), has shown promising results both in simulations and an initial prototype. Multiple wedges, each covering a different range of fan angle, are moved in the axial direction to change their attenuating thickness as seen in an axial slice. We report on an implementation of a filter with precision components and a control algorithm targeted for operation on a table-top system. Algorithms for optimizing wedge position and mA modulation and for correcting bowtie-specific beam-hardening artifacts are proposed. In experiments, the error between expected and observed bowtie transmission was ∼2% on average and ∼7% at maximum for a chest phantom. Within object boundaries, the observed flux dynamic ranges of 42, for a chest phantom, and 25, for an abdomen phantom were achieved, corresponding to a reduction factor of 5 and 11 from the object scans without the bowtie. With beam hardening correction, the mean CT number in soft tissue regions was improved by 79 HU on average, and deviated by 7 HU on average from clinical scanner CT images. The implemented piecewise-linear attenuator is able to dynamically adjust its thickness with high precision to achieve flexible flux control.
AB - A dynamic bowtie filter can modulate flux along both fan and view angles for reduced dose, scatter, and required detector dynamic range. Reducing the dynamic range requirement is crucial for photon counting detectors. One approach, the piecewise-linear attenuator (Hsieh and Pelc, Med Phys 2013), has shown promising results both in simulations and an initial prototype. Multiple wedges, each covering a different range of fan angle, are moved in the axial direction to change their attenuating thickness as seen in an axial slice. We report on an implementation of a filter with precision components and a control algorithm targeted for operation on a table-top system. Algorithms for optimizing wedge position and mA modulation and for correcting bowtie-specific beam-hardening artifacts are proposed. In experiments, the error between expected and observed bowtie transmission was ∼2% on average and ∼7% at maximum for a chest phantom. Within object boundaries, the observed flux dynamic ranges of 42, for a chest phantom, and 25, for an abdomen phantom were achieved, corresponding to a reduction factor of 5 and 11 from the object scans without the bowtie. With beam hardening correction, the mean CT number in soft tissue regions was improved by 79 HU on average, and deviated by 7 HU on average from clinical scanner CT images. The implemented piecewise-linear attenuator is able to dynamically adjust its thickness with high precision to achieve flexible flux control.
KW - dynamic bowtie filter
KW - dynamic range reduction
KW - fluence field modulation
KW - photon counting detector
UR - http://www.scopus.com/inward/record.url?scp=85049262714&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85049262714&partnerID=8YFLogxK
U2 - 10.1117/12.2293525
DO - 10.1117/12.2293525
M3 - Conference contribution
AN - SCOPUS:85049262714
T3 - Progress in Biomedical Optics and Imaging - Proceedings of SPIE
BT - Medical Imaging 2018
A2 - Schmidt, Taly Gilat
A2 - Chen, Guang-Hong
A2 - Lo, Joseph Y.
PB - SPIE
T2 - Medical Imaging 2018: Physics of Medical Imaging
Y2 - 12 February 2018 through 15 February 2018
ER -